1. Field of the Invention
The present invention relates to communication systems, transmitting devices, transmitting methods, receiving devices, and receiving methods. More particularly, the present invention relates to a communication system, a transmitting device, a transmitting method, a receiving device, and a receiving method enabling suppression of radiated power generated by communication via a line-to-line coupling.
2. Description of the Related Art
Types of communication system for transmitting and receiving data include a contact type and a contactless type. The contact communication systems exchange data via electric contact points such as connectors. In contrast, the contactless communication systems do not require such electronic contact points.
Adhesion of extraneous materials, such as dust, moisture, and oil, to electric contact points or formation of oxide film on the electric contact points may make contact communication systems unable to transmit and receive signals correctly. In addition, static electricity may destroy internal circuits, when electric contact points are exposed. In order to prevent such circumstances, highly-accurate processing is performed to form the shapes of the electric contact points.
On the other hand, contactless communication systems are free from the above-described problems since contactless communication systems require no electric contact points.
In contactless communication methods, communication is performed via, for example, electromagnetic fields, capacitances, microwaves, or laser beams. A transfer rate higher than a few hundred Mbps (megabits per second), particularly that exceeding 1 Gbps, is achieved only in communication via laser beams or microwaves.
However, devices used for communication via laser beams are still expensive. Miniaturization of such devices is also difficult. In addition, in communication via microwaves, radiated power has to be controlled so as not to exceed a value determined by the Radio Law of each country.
One of the contactless communication methods that implement communication at a high transfer rate employs a line-to-line coupling generated by bringing microstrip lines closer so that they face each other (hereinafter, referred to as “line-to-line coupling of the microstrip lines”).
In communication via the line-to-line coupling of microstrip lines, radiated power is much smaller than that generated when a radio wave (e.g., microwave) is radiated using an antenna (i.e., a microstrip antenna) as suggested in Japanese Unexamined Patent Application Publication No. 07-297625. However, it may be difficult to control the radiated power so as not to exceed values determined by laws without taking any measures. When communication is performed at a high transfer rate, the radio wave (i.e., electromagnetic wave) radiated by the line-to-line coupling of the microstrip lines has a frequency band between 322 MHz and 10 GHz. In Japan, the radiated power in this frequency band has to be controlled so as not to exceed 35 μV.